The present invention relates to an apparatus for making a gap in a moving stream of overlapped signatures.
In the printing industry there is a need to form gaps in streams of overlapped signatures moving on conveyors. For example, signatures from a printing press or folder travel in an overlapped or shingled stream. In order to stack or bundle the signatures in groups of a predetermined size it is desirable to make a gap in the moving stream.
Various stream interrupters or gap makers have been used in the past. Most of these gap makers temporarily arrest some of the signatures while those signatures ahead continue to advance. Once the gap is formed, the temporarily halted signatures are released, and they again move with the conveyor. The stream of signatures may be stopped by abruptly interposing a finger or the like to stop the stream. Devices of this sort are shown in U.S. Pat. Nos. 3,373,666 and 3,313,221. Other stream interrupters pinch the signatures between a rail or rails fixed above the conveyor and a rail or rails which move(s) upward from below the conveyor. See, e.g., U.S. Pat. Nos. 3,708,162 and 3,149,834. U.S. Pat. No. 3,724,840 shows a stream interrupter having both features. Once a gap is made in the stream, the signatures are released onto the conveyor.
The prior art stream interrupters or gap makers have a tendency to mutilate the lead signature of a group when that signature is stopped and then released onto the conveyor. Specifically, when a signature at the front of a group is temporarily stopped, the rear edge of that signature may be curled under because of contact with the moving conveyor. Further, the outside page of the front signature of a stopped group may be stripped from the signature when it is released back onto the moving conveyor. Moreover, in many of these gap makers the pressure applied to the leading signatures of a group to stop them is uneven across the width of the conveyor. Since the conveyor continues to move and therefore pulls on the trailing edges of the stopped signatures, especially those at the front of a group, there is a tendency to skew the leading signatures of a group.